Typical internal combustion engines having turbochargers operate by providing exhaust gas energy to drive one or more turbines, each of which is connected to and drives a respective air compressor. The compressors provide a charge, which may be cooled and which is provided to the engine cylinders during operation.
Internal combustion engines having more than one turbocharger connected in parallel are known, it is challenging to appropriately size the one, two or three turbochargers to achieve the desired power of the engine while also maintaining exhaust temperatures at a sufficiently low level to help reduce NOx emissions. One example of an engine having three turbochargers connected in parallel can be seen in Great Britain Patent Pub. No. GB 2220987B. This reference describes an engine having three turbochargers connected in parallel across the engine's intake and exhaust collectors. One of the three turbochargers is always connected to the engine, while the remaining two can be cut-in or cut-out depending on engine load operating conditions. While the solution may be at least partially effective in using appropriately sized turbochargers for the engine, there are efficiency losses in the way the turbochargers are connected in that pressure drops are introduced, and exhaust pulses are diminished or destroyed in the complex exhaust and intake piping used to connect the turbochargers with the rest of the engine. This can result in lower engine efficiency, which in turn increases fuel consumption and heat rejection in the engine, which can in turn also affect engine emissions.